Code 28, Pressure Switch Manifold Fault: Notes

The Pressure Switch Manifold (PSM), also referred to as fluid pressure switch assembly, is actually 5 pressure switches combined into one unit and mounted on the transmission valve body. The PCM/TCM supplies battery voltage to the PSM on 3 separate wires. By grounding one or more of these circuits through various combinations of switches inside the pressure switch manifold, the PCM/TCM detects what gear range has been selected by the vehicle operator.

1. This test compares the indicated range to the range actually selected.
2. This test checks for correct voltage from the PCM/TCM to the transmission pass-thru connector.
3. This test will detect a short to ground in any one of the 3 PSM range circuits.